1. Field of the Invention
The present invention relates to a radiation imaging apparatus, a radiation imaging system, and a program that are suitably used, e.g., in medical diagnosis, industrial non-destructive inspection, and the like. In addition, in the present specification, it is assumed that “radiations” include electromagnetic waves, such as an X-ray, and a γ-ray, an α-ray, and a β-ray.
2. Description of the Related Art
Radiation imaging systems that have been installed in hospitals, clinics, or the like are categorized into an analogue and a digital radiographing method. In the analogue radiographing method, radiations such as X-rays are irradiated onto a patient and a film is exposed by the radiations that have passed through the patient. In the digital radiographing method, radiations that have passed through the patient are converted into electric signals, i.e., digital data so as to obtain image data.
The digital radiographing method includes the CR (Computed Radiography) method and the FPD (Flat Panel Detector) method. In the CR method, a radiation image is temporarily stored in photostimulable phosphors made mainly of BaFBr, and then scanned by a laser beam so as to obtain digital data. In the FPD method, radiations that have passed through the patient are converted into visible light, by means of a scintillator such as Gd2O2S:Tb or CsI:Tl; then, the visible light is converted into an electric signal, by means of a photoelectric conversion element made mainly of amorphous silicon semiconductor. In addition, some of FPD-method radiation imaging apparatuses utilize, instead of a scintillator, a conversion device, made of, e.g., amorphous selenium, that converts radiations directly into an electric signal. The former and the latter are referred to as the indirect and the direct FPD, respectively.
In recent years, it has been desired that moving imaging, e.g., gastric fluoroscopic radiographing, angiographing during operation, and the like, which have been implemented by means of an image intensifier (I.I.), are carried out by means of the FPD. That is because, while the I.I. has problems of fringe-portion image distortion, halation in the case of irradiating strong radiations, and sensitivity deterioration due to long-term use, the FPD does not pose such problems and, in recent years in particular, has become relatively inexpensive to produce. In addition, although, as an apparatus that can be digitized, the CR-method apparatus has become widespread since 1980, it poses, in operational principle, some disadvantage in radiographing a moving image. In other words, it is conceivable that the FPD method, which has functions of both the CR method for still images and the I.I. method for moving images, becomes a mainstream in digitization in medicine in the future. The FPD-method digitization largely improves hospital workflows and facilitates the recording and printing of radiographic data; in addition to that, the FPD-method digitization can considerably contribute to improvement of diagnosis efficiency, by making full use of an advanced computer-aided image processing technique. In the second half of 1990, upright type and decubitus type radiation imaging apparatuses were marketed in which the FPD method were employed, and in recent years, X-ray imaging apparatuses capable of radiographing moving images have been proposed and marketed.